Methods for embedding information in data without increasing the amount of the data exist, for example, changing the lowest bit or low-order two bits of digital audio data into information to be embedded. The method simply replaces lower bits of digital audio data with information to be embedded, taking advantage of the fact that the lower bits do not significantly affect the quality of sound. Thus, when the digital audio data is played back, the digital audio data with the information embedded therein is output as it is without restoring the lower bits. That is, since it is difficult to restore the lower bits, in which information is embedded, into the original digital audio data, and the lower bits do not significantly affect the quality of sound, the digital audio data is output with the information embedded therein.
According to the method described above, however, data that differs from the original data is output. Thus, considerable effect is exerted upon the sound quality when the data is audio data or upon the picture quality when the data is video data.